In a display device such as a smartphone or a tablet, a touch panel is provided. This allows a user to make an operation by lightly touching a screen of the display device equipped with the touch panel. The user, however, sometimes touches a part that he/she did not intend to touch during an operation, thereby making an input error. The user therefore has to gaze the screen while making an operation.
As a technique for facilitating operations of a user, for example, a cover attached to a portable device equipped with a touch screen is described in Patent Document 1 indicated below. This cover has an opening or a button, and is attached at such a position that the same covers at least a part of a user interface of the portable device.
Further, Patent Document 2 indicated below discloses an external cover for a tablet smartphone equipped with a touch screen. The document discloses that a keyboard is formed on this external cover, and this keyboard is caused to correspond to a virtual keyboard displayed on the touch screen.